Advocate with professional attitude (7)
I believe the answer is:
propose
'advocate' is the definition.
(thesaurus)
'with professional attitude' is the wordplay.
'with' is a charade indicator (letters next to each other).
'professional' becomes 'pro' ('pro' can be a synonym of 'professional').
'attitude' becomes 'pose' (I've seen this before).
'pro' next to 'pose' is 'PROPOSE'.
(Other definitions for propose that I've seen before include "Put forward a plan" , "Offer for consideration" , "Suggest - make an offer" , "Intend" , "Tender" .)